Vibrating structure gyrometer with at least one tuning fork

ABSTRACT

Vibrating structure gyrometer with at least one tuning fork, produced by micro-machining from a thin plate, the said tuning fork comprising a pair of mobile inertial assemblies (EIM 1 , EIM 2 ) linked by a coupling assembly ( 1 ). A tuning fork comprises two controlled electrodes ( 9, 9 ′) for equilibration of the sense resonator and electrostatic adjustment of the frequency of the sense resonator along the sense axis y which are respectively associated with the two mobile inertial assemblies (EIM 1 , EIM 2 ) of the said tuning fork, and control means (UCE) adapted for applying two respective continuous electrical voltages V 1  and V 2  to the said two electrodes ( 9, 9 ′) simultaneously satisfying the relations: 
     
       
         
           
             
               
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The invention pertains to a vibrating structure gyrometer with at leastone tuning fork, produced by micro-machining from a thin plate.

Tuning fork gyrometers are known, as illustrated in FIG. 1. Two mobileinertial assemblies EIM1 and EIM2 form a tuning fork, are suspended on arigid framework CR, and possess two degrees of freedom along the x and yaxes respectively dubbed the drive axis and the sense axis. The mobileinertial assemblies EIM1, EIM2 are linked to the rigid framework CR bystiffness elements Kx1 and Kx2 in the drive direction x and by stiffnesselements Ky1 and Ky2 in the sense direction y. Each mobile inertialassembly EIM1, EIM2 comprises one or more masses.

The two mobile inertial assemblies EIM1 and EIM2 are mechanicallycoupled together by a coupling assembly of stiffness k_(cx). in thedrive direction x and of stiffness k_(cy) in the sense direction y. Sucha gyrometer is, for example, described in document WO2004/042324(THALES).

Such a gyrometer exhibits 2 useful modes of vibration:

-   -   a mode of frequency fx in which the two mobile inertial        assemblies EIM1 and EIM2 vibrate in phase opposition along the        drive axis x; this mode is dubbed the drive mode; and    -   a mode of frequency fy in which the two mobile inertial        assemblies EIM1 and EIM2 vibrate in phase opposition along the        sense axis y; this mode is dubbed the sense mode.

As illustrated in FIG. 2, the two mobile inertial assemblies EIM1 andEIM2 are excited on the drive mode of resonance, according to which modethey vibrate in phase opposition in the direction of the x axis. Aslaving loop, not represented in the figure, makes it possible tomaintain the drive frequency at the resonant frequency f_(x) of thedrive mode as well as to keep the amplitude of this motion constant.

In the presence of a rotation speed Ω, directed along a third axis zsuch that the reference system (y, x, z) is right-handed, the Coriolisforces cause a coupling between the drive resonator and the senseresonator bringing about a vibratory motion of each of the two mobileinertial assemblies EIM1 and EIM2 along the sense axis y, as illustratedin FIG. 3. Each mobile inertial assembly EIM1, EIM2 comprises severalmasses, for example two, one involved in the drive resonator, but bothinvolved in the sense resonator. Stated otherwise, in a simplifiedmanner, the sense resonator comprises the two mobile inertial assembliesEIM1, EIM2 and the elements with stiffnesses along the sense axis y, andthe drive resonator comprises the two mobile inertial assemblies EIM1,EIM2 and the elements with stiffnesses along the drive axis x.

The motions of the two mobile inertial assemblies EIM1 and EIM2 alongthe sense axis y are in phase opposition and the useful motion may bedefined by the half-difference of the sense motions y₁ and y₂ of eachmobile inertial assembly. This motion is henceforth dubbed thedifferential sense motion y_(diff). It may be defined by

$y_{diff} = {\frac{y_{1} - y_{2}}{2}.}$

This motion is also of resonant frequency f_(x) along the drive axis x.The amplitude of this differential sense motion is proportional to therotation speed.

For tuning fork gyrometers operating in open loop, the amplitude of thesense motion y_(diff) is measured directly so as to obtain rotationspeed information.

For gyrometers operating in closed loop, the differential sense motiony_(diff) is slaved to zero by electrostatic force balance along thesense axis y. The gyrometer output information is then given by thedifferential feedback voltage necessary for the cancellation of thedisplacement. The conventional scheme for such slaving is, for example,illustrated and described in European patent EP 1 579 176 81 (THALES).

It is well known to the person skilled in the art that the imperfectionsin production of a gyrometer lead to errors in the information deliveredas output by the gyrometer. Most of these imperfections must becompensated by equilibrating the gyrometer by equilibrating thegyrometer.

It is known to carry out this compensation by removing material locally,for example by laser ablation, so as to modify the distribution of massor of stiffness. This process is generally expensive to implement on agyrometer micro-machined from a thin silicon plate, whose sense anddrive motions lie in the plane of the substrate.

On gyrometers micro-machined from silicon, the compensation may becarried out in an electrical manner, on the basis of electrostaticforces controllable by controlled electrical voltages. Such pyrometersgenerally employ electrostatic means, notably controlled electrodes,capable of compensating two types of defects:

-   -   the mechanical coupling between the drive mode and the sense        mode, from which the so-called quadrature bias originates, and    -   the discrepancy in frequencies between drive mode and the sense        mode.

An exemplary embodiment for compensating for the quadrature bias of aplanar micro-machined vibrating gyrometer whose drive and sense motionsare linear and situated in the plane of the substrate is described inpatent application WO 2007/068649 (THALES).

However, such compensations do not make it possible to compensate forthe effects of the mass and stiffness asymmetries between the twobranches of the tuning fork.

In fact, a tuning fork gyrometer whose two branches are asymmetric issensitive to linear accelerations.

Indeed if the branches of the tuning fork are perfectly symmetric, themotions of each mobile inertial assembly of a branch of the tuning forkcaused by linear accelerations remain perfectly symmetric. On account ofthe differential architecture of the tuning fork gyrometer, this motion,has no detectable effect and therefore cannot disturb the gyrometeroutput.

On the other hand, in the presence of asymmetries of mass or ofstiffness between the two mobile inertial assemblies of the branches ofthe tuning fork, the linear accelerations along the sense axis y thencause non-symmetric motions along the sense axis y of the two mobileinertial assemblies. The effect of these asymmetric motions is thendetectable and provokes a disturbance of the gyrometer output signal.

This disturbance may be manifested as a sensitivity of the output of thegyrometer to static accelerations or to dynamic accelerations along thesense axis y.

The information S delivered as output by the gyrometer, expressed indegrees/hour (deg/h or °/h), may be put into the form of the followingrelation:

S=S _(O) +c _(u)γ_(y)

in which:

-   S_(O) represents the gyrometer output signal in the absence of    acceleration, in deg·h⁻¹,-   γ_(y) represents a static or dynamic linear acceleration along the    sense axis y, in G, G being equal to 9.81 m·s⁻²,-   c_(y) represents the sensitivity of the output S to the acceleration    γ_(y), in deg·h⁻¹·G⁻¹, and

c _(y) =aδk _(y) +bδm _(y),

-   a being a sensitivity coefficient, in deg·h⁻¹·G⁻¹·N·m⁻¹ that may    possibly vary as a function of the frequency of the acceleration,-   b being a sensitivity coefficient, in deg·h⁻¹·G⁻¹·kg⁻¹ that may    possibly vary as a function of the frequency of the acceleration,-   δm=m1−m2 representing the discrepancy of masses between the two    branches of the tuning fork, in kg, and-   δk=k1−k2 representing the discrepancy of stiffnesses between the two    branches of the tuning fork, in N·m⁻¹.

The reduction in the sensitivity to vibrations or to linearaccelerations along the sense axis y may be obtained by equilibration ofthe two branches of the tuning fork.

On certain gyrometers with metallic or quartz tuning fork, thisequilibration is produced through local material ablation consisting increating an asymmetry of mass or of stiffness that is opposite to theinitial asymmetries of the tuning fork. This process is generallyexpensive and difficult to implement on silicon micro-machinedgyrometers of small size.

It is also possible to use controlled electrostatic forces making itpossible to create an asymmetry in electrostatic stiffness that iscontrolled by an electrical signal which opposes the initialasymmetries. Such processes are applied to gyrometers with vibratingshells or vibrating annulus.

An aim of the invention is to compensate for the asymmetries in massesor in stiffness of the sense resonator or tuning fork of a silicontuning fork gyrometer, at reduced cost, and with improved precision.

According to one aspect of the invention, there is proposed a vibratingstructure gyrometer with at least one tuning fork, produced bymicro-machining from a thin plate, the said tuning fork comprising apair of mobile inertial assemblies linked by a coupling assembly, onembbile inertial assembly being furnished with first stiffness elementsessentially deformable in the plane of the plate along an drive axis xand with second stiffness elements essentially deformable in the planeof the plate along a sense axis y substantially perpendicular to the xaxis. The gyrometer comprises, furthermore, for the tuning fork, twofirst controlled electrodes for electrostatic excitation along the driveaxis x which are respectively associated with the two mobile inertialassemblies, two second controlled electrodes for capacitive detection ofthe drive motion along the drive axis x which are respectivelyassociated with the two mobile inertial assemblies, and two thirdcontrolled electrodes for capacitive detection of the drive motion alongthe sense axis y which are respectively associated with the two mobileinertial assemblies. When the sense motion is slaved by electrostaticforce balance, the gyrometer comprises two controlled electrodes makingit possible to apply the electrostatic feedback force necessary for theslaving of the sense motion.

The gyrometer also comprises:

two fourth controlled electrodes for equilibration of the senseresonator and electrostatic adjustment of the frequency of the senseresonator along the sense axis y which are respectively associated withthe two mobile inertial assemblies of the said tuning fork, andcontrol means adapted for applying two respective continuous electricalvoltages V₁ and V₂ to the said two fourth electrodes simultaneouslysatisfying satisfying the relations:

${V_{1}^{2} + V_{1}^{2}} = \frac{2\left( {f_{y\; \_ \; {initial}} - f_{y\; \_ \; {final}}} \right)}{\mu_{f}}$and${V_{1}^{2} - V_{2}^{2}} = \frac{c_{y\; \_ \; {initial}}}{a\; \lambda_{f}}$

in which:

-   f_(y) _(—) _(initial) represents the initial resonant frequency,    when the electrical voltages V₁ and V₂ are zero, of the sense mode    along the sense axis y, in Hz,-   f_(y) _(—) _(final) represents the final resonant frequency of the    sense mode along the sense axis y to be adjusted, in Hz, and-   μ_(f) represents a coefficient of sensitivity of the frequency of    the sense mode to the square of the electrical voltage applied to    the said fourth electrodes (9, 9′), in Hz·V⁻²,-   c_(y) _(—) _(initial) represents the initial sensitivity of the    gyrontieter, when the two electrical voltages V₁ and V₂ are zero, to    linear accelerations along the sense axis y in deg·h⁻¹·G⁻¹,-   a represents a coefficient characterizing the influence of a    discrepancy in stiffness between the two branches of the tuning fork    on the sensitivity of the gyrometer to linear accelerations along    the y axis, in deg·h⁻¹·G⁻¹·N⁻¹·m, that may possibly vary as a    function of the frequency of the acceleration,-   λ_(f) represents an electrostatic stiffness coefficient dependent on    the said fourth electrodes (9, 9′) in N·m⁻¹·V⁻²,-   V₁ and V₂ are expressed in Volts, and-   G equals 9.81 m·s⁻².

Such a gyrometer is thus, at reduced cost, compensated, in such a way asto greatly limit, or indeed cancel, the asymmetries of masses or ofstiffness of the tuning fork or tuning forks.

Moreover, the precision is thus further improved, since the adjustmentof the discrepancy in frequencies between the sense mode and drive modeallows better control of the gyrometric coupling between the sense modeand the drive mode and thus makes it possible to circumvent thedispersions caused by certain manufacturing defects in this coupling.

The sense motion of the sense resonator may be cancelled by slaving byelectrostatic balance of forces, the said final resonant frequency f_(y)_(—) _(final) is then equal to the frequency f_(x) of the drive modealong the drive axis x, and the equalization of the two frequencies maybe achieved either by using a feedback loop to control the said fifthelectrodes, or by open-loop control of the said fifth electrodes.

In another embodiment, in which the sense motion of the sense resonatoris in open loop, the said final resonant frequency _(fy) _(—) _(final)is equal to the sum of the frequency fx of the mode of the drive modealong the drive axis x and of a predetermined frequency discrepancyΔf_(y).

The invention will be better understood on studying a few embodimentsdescribed by way of wholly non-limiting examples and illustrated by theappended drawings in which:

FIGS. 1, 2 and 3 schematically illustrate a tuning fork gyrometer andits operation, of the prior art; and

FIG. 4 illustrates an embodiment of a vibrating structure gyrometer withat least one tuning fork, produced by micro-machining from a thin plate,according to one aspect of the invention.

In the various figures, elements having identical references aresimilar.

In FIG. 4 is schematically represented a vibrating structure gyrometerwith tuning fork, produced by micro-machining from a thin plate.

Of course, the invention also applies to a vibrating structuregyrometer, produced by micro-machining from a thin plate, comprising anarbitrary number of tuning forks.

Two mobile inertial assemblies EIM1 and EIM2 linked by a couplingassembly 1 form a tuning fork, and are suspended on a rigid frameworkCR. The two mobile inertial assemblies EIM1 and EIM2 possess two degreesof freedom along the axes x and y respectively dubbed the drive axis andthe sense axis. The drive axe x and the sense axis y are substantiallyorthogonal.

A mobile inertial assembly is, for example, such as described in patentapplication WO2004/042324 (THALES).

Each mobile inertial assembly EIM1, EIM2 is respectively furnished withfirst stiffness elements 2, 2′ essentially deformable in the plane ofthe plate along the drive axis x. Furthermore, each mobile inertialassembly EIM1, EIM2 is respectively furnished with second stiffnesselements 3, 3′ essentially deformable in the plane of the plate alongthe sense axis y.

In a conventional manner, the gyrometer comprises an electronic controlunit UCE, and two first controlled electrodes 4, 4′ for electrostaticexcitation along the drive axis x which are respectively associated withthe two mobile inertial assemblies EIM1, EIM2.

Two second controlled electrodes 5, 5′ for capacitive detection of thedrive motion along the drive axis x are respectively associated with thetwo mobile inertial assemblies EIM1, EIM2.

Moreover, two third controlled electrodes 6, 6′ for capacitive detectionof the drive motion along the sense axis y are respectively associatedwith the two mobile inertial assemblies EIM1, EIM2.

When the sense motion is slaved by electrostatic force balance, thegyrometer comprises two electrodes 7 and 7′ associated with the twomobile assemblies EIM1 and EIM2 and making it possible to apply theelectrostatic feedback force necessary for the slaving of the sensemotion.

Two controlled optional extra electrodes 8, 8′ can serve to compensatethe quadrature bias.

The gyrometer also comprises two fourth controlled electrodes 9, 9′ forequilibration of the sense resonator and electrostatic adjustment of thefrequency of the sense resonator along the sense axis y which arerespectively associated with the two mobile inertial assemblies (EIM1,EIM2) of the said tuning fork.

An electronic control unit UCE manages the operation of the gyrometer.

The electronic control unit UCE is adapted for applying two respectivecontinuous electrical voltages V₁ and V₂ to the said two fourthelectrodes 9, 9′ satisfying the relation

${{V_{1}^{2} + V_{2}^{2}} = \frac{2\left( {f_{y\; \_ \; {initial}} - f_{y\; \_ \; {final}}} \right)}{\mu_{f}}},$

in which:

-   f_(y) _(—) _(initial) represents the initial resonant frequency,    when the electrical voltages V₁ and V₂ are zero, of the sense mode    along the sense axis y, in Hz,-   f_(y) _(—) _(final) represents the final resonant frequency of the    sense mode along the sense axis y to be adjusted, in Hz, and-   μ_(f) represents a coefficient of sensitivity of the frequency of    the sense mode to the square of the electrical voltage applied to    the said fourth electrodes, in Hz·V⁻².

Indeed, by applying electrical voltages V₁ and V₂ to each of the twofourth equilibration electrodes 9 and 9′, negative electrostaticstiffnesses k_(el1) and k_(el2), in N·m⁻¹, along the sense axis y, arecreated on each of the two branches EIM1 and EIM2 of the tuning fork:

k _(el1) =−λV ₁ ², and

k _(el2) =−λV ₂ ²

λ representing a coefficient which characterizes the proportionalitybetween the electrostatic stiffness and the square of the electricalvoltage applied to the fourth electrodes 9, 9′, in N·m⁻¹·V⁻².

The effect of these variations in stiffnesses is to create a discrepancyin stiffnesses Δk between the two branches EIM1 and EIM2 of the tuningfork, in proportion to the difference of the squares of the electricalvoltages V₁ and V₂ applied Δk satisfying the following relation:

Δk=−λ(V ₁ ² −V ₂ ²)

The effect of these stiffness variations is also to decrease theresonant frequency of the sense mode along the sense axis y inproportion to the sum of the squares of the voltages applied, accordingto the following relation:

${f_{y\; \_ \; {final}} = {f_{y\; \_ \; {initial}} - {\frac{\mu_{f}}{2}\left( {V_{1}^{2} + V_{2}^{2}} \right)}}},$

Hence, to attain the final or desired value f_(y) _(—) _(final) of theresonant frequency of the sense mode along the sense axis y, theelectrical voltages V₁ and V₂ to be applied to the fourth electrodes 9,9′ must comply with the following relation:

${V_{1}^{2} + V_{2}^{2}} = \frac{2\left( {f_{y\; \_ \; {initial}} - f_{y\; \_ \; {final}}} \right)}{\mu_{f}}$

In order that the trim or frequency adjustment may be possible, the term(f_(y) _(—) _(initial)−f_(y) _(—) _(final)) must always be positive.This is achieved by a dimensioning of the gyrometer which guaranteesthat the frequency discrepancy (f_(y) _(—) _(initial)−f_(y) _(—)_(final)) always remains positive, despite the manufacturing spread.

The discrepancy in stiffness Δk between the two branches EIM1 and EIM2of the tuning fork, has the effect of creating a sensitivity S_(y) ofthe gyrometer to linear accelerations along the sense axis y, satisfyingthe relation s_(y)=aλ(V₁ ²−V₂ ²)γ_(y), and that may be subtracted fromthe initial output S equal to c_(y) _(—) _(initial)·γ_(y).

Thus, an output S satisfying the following relation is obtained:

S=c _(y) _(—) _(initial)·γ_(y) −aλ(V ₁ ² −V ₂ ²)γ_(y)

The output S can thus be cancelled by adjusting the voltages V₁ and V₂in such a way that the following condition is fulfilled:

$\begin{matrix}{{V_{1}^{2} - V_{2}^{2}} = \frac{c_{y\; \_ \; {initial}}}{a\; \lambda}} & \left( {{equation}\mspace{14mu} 1} \right)\end{matrix}$

The term c_(y) _(—) _(initial) which represents the initial sensitivityof the gyrometer to acceleration may be measured for example during thecalibration of the gyrometer.

The difference of the squares of the electrical voltages V₁ and V₂allows the electronic control unit UCE to control the sensitivity of thegyrometer to vibrations and the sum of the squares of the electricalvoltages V₁ and V₂ allows this electronic control unit UCE to controlthe frequency of the sense mode.

For example, it may be considered that the maximum electrical voltagesapplicable to the fourth electrodes 9, 9′ are 20 V, and that thecoefficients a, λ_(f), and μ_(f) produce the following conditions:

aλ _(f)≈0.5°/h/g/V ², and

μ_(F)≈0.79 Hz/V ²

The electrical voltages V₁ and V₂, necessary for determined values ofc_(y) _(—) _(initial) and of f_(y) _(—) _(initial)−f_(y) _(—) _(final),then satisfy the following relations:

$V_{1}^{2} = {\frac{1}{2}\left( {\frac{f_{y\; \_ \; {initial}} - f_{y\; \_ \; {final}}}{0.79} + \frac{c_{{\gamma\_}\; {initial}}}{0.5}} \right)}$$V_{2}^{2} = {\frac{1}{2}\left( {\frac{f_{y\; \_ \; {initial}} - f_{y\; \_ \; {final}}}{0.79} - \frac{c_{\gamma \; \_ \; {initial}}}{0.5}} \right)}$

The electrical voltages V₁ and V₂ lie between 0 V and 20 V.f_(y) _(—) _(initial)−f_(y) _(—) _(final) is always positive.On the other hand, c_(y) _(—) _(initial) may be positive or negative.

By assuming c_(y) _(—) _(intial) positive, the following two conditionsmust then be complied with:

${\frac{1}{2}\left( {\frac{f_{y\; \_ \; {initial}} - f_{y\; \_ \; {final}}}{0.79} + \frac{c_{\gamma \; \_ \; {initial}}}{0.5}} \right)} \leq 20^{2}$${\frac{1}{2}\left( {\frac{f_{y\; \_ \; {initial}} - f_{y\; \_ \; {final}}}{0.79} - \frac{c_{{\gamma\_}\; {initial}}}{0.5}} \right)} \geq 0$

or else:

${0.79\frac{c_{\gamma \; \_ \; {initial}}}{0.5}} \leq {f_{y\; \_ \; {initial}} - f_{y\; \_ \; {final}}} \leq {0.79 \cdot \left( {{2 \cdot 20^{2}} - \frac{c_{{\gamma\_}\; {initial}}}{0.5}} \right)}$

Assuming c_(y) _(—) _(initial) negative, the same conditions areobtained.

The gyrometer. is dimensioned in such a way that the discrepancy f_(y)_(—) _(initial)−f_(y) _(—) _(final) complies with this doubleinequality.

The information S delivered as output by the gyrometer, expressed indegrees/hour (deg/h or °/h), may be put into the form of the followingrelation:

S=S _(O) +c _(y)γ_(y)

The invention is based on the fact that the sensitivity term c_(y)evolves linearly as a function of the difference of the squares of thevoltages V₁ and V₂ applied to each of the fourth electrodes. It istherefore possible to cancel this term by applying an appropriate valueof V₁ ²−V₂ ² to these electrodes.This dependency of c_(y) on V₁ ²−V₂ ² may be demonstrated in atheoretical manner on the basis of the following two elements:

the coefficient c_(y) depends linearly on the asymmetries of stiffnessand of mass δm=m1−m2 and δk=k1−k2 of the tuning fork. It is thereforepossible to put the coefficient c_(y) into the following formc_(y)=aδk+bδm.

Moreover, an electrostatic stiffness asymmetry δk_(yel) can be createdartificially by applying two DC voltages V₁ and V₂ to the two fourthelectrodes. This stiffness is proportional to the difference of thesquares of the voltages applied and can therefore be written in theform: δk_(yel)=λ(V₂ ²−V₁ ²)Thus by applying a voltage V₁ and V₂, the sensitivity term c_(y) ismodified in the following manner: c_(y)=a(δk+δk_(yel))+bδmOr else: c_(y)=a(δk+λ(V₂ ²−V₁ ²))+bδmAll these elements mentioned previously make it possible to bolster thefact that the sensitivity to acceleration term c_(y) evolves linearly asa function of the square of the voltages V₁ and V₂ applied to each ofthe fourth electrodes.But to determine what value of V₁ ²−V₂ ² cancels the sensitivity termc_(y), it is wholly unnecessary to determine the coefficients a, b, λseparately.We proceed in the following manner:For a value of V₁ ²−V₂ ² equal to zero, the value of the sensitivitycoefficient c_(y) is determined experimentally. Accordingly, the sensoris subjected to several acceleration levels, and the sensor output S ismeasured for each level. The slope of the evolution of S as a functionof the level of acceleration gives the value of the coefficient c_(y).

The measurement of c_(y) is repeated for nonzero values of V₁ ²−V₂ ²(for example for two other values).

This therefore yields a curve of the evolution of c_(y) as a function ofV₁ ²−V₂ ². The value of V₁ ²−V₂ ² which cancels the sensitivity toacceleration can then be determined precisely by interpolation or byextrapolation.

1. Vibrating structure gyrometer with at least one tuning fork, producedby micro-machining from a thin plate, the said tuning fork comprising apair of mobile inertial assemblies (EIM1, EIM2) linked by a couplingassembly (1), one mobile inertial assembly (EIM1, EIM2) being furnishedwith first stiffness elements (2, 2′) essentially deformable in theplane of the plate along an drive axis x and with second stiffnesselements (3, 3′) essentially deformable in the plane of the plate alonga sense axis y substantially perpendicular to the x axis, the gyrometercomprising, furthermore, for the tuning fork, two first controlledelectrodes (4, 4′) for electrostatic excitation along the drive axis xwhich are respectively associated with the two mobile inertialassemblies (EIM1, EIM2), two second controlled electrodes (5, 5′) forcapacitive detection of the drive resonator along the drive axis x whichare respectively associated with the two mobile inertial assemblies(EIM1, EIM2), two third controlled electrodes (6, 6′) for capacitivedetection of the drive motion along the sense axis y which arerespectively associated with the two mobile inertial assemblies (EIM1,EIM2), and two fourth controlled electrodes (9, 9′) for equilibration ofthe sense resonator and electrostatic adjustment of the frequency of thesense resonator along the sense axis y which are respectively associatedwith the two mobile inertial assemblies (EIM1, EIM2) of the said tuningfork, characterized in that it comprises: control means (UCE) adaptedfor applying two respective continuous electrical voltages V₁ and V₂ tothe said two fourth electrodes (9, 9′) simultaneously satisfying therelations:${V_{1}^{2} + V_{1}^{2}} = \frac{2\left( {f_{y\; \_ \; {initial}} - f_{y\; \_ \; {final}}} \right)}{\mu_{f}}$and${V_{1}^{2} - V_{2}^{2}} = \frac{c_{y\; \_ \; {initial}}}{a\; \lambda_{f}}$in which: f_(y) _(—) _(initial) represents the initial resonantfrequency, when the electrical voltages V₁ and V₂ are zero, of the sensemode along the sense axis y, in Hz, f_(y) _(—) _(final) represents thefinal resonant frequency of the sense mode along the sense axis y to beadjusted, in Hz, and μ_(f) represents a coefficient of sensitivity ofthe frequency of the sense mode to the square of the electrical voltageapplied to the said fourth electrodes (9, 9′), in Hz·V², c_(y) _(—)_(initial) represents the initial sensitivity of the gyrometer, when thetwo electrical voltages V₁ and V₂ are zero, to linear accelerationsalong the sense axis y in deg·h⁻¹·G⁻¹, a represents a coefficientcharacterizing the influence of a discrepancy in stiffness between thetwo branches of the tuning fork on the sensitivity of the gyrometer tolinear accelerations along the y axis, in deg·h⁻¹·G⁻¹·N⁻¹·m, possiblyable to vary as a function of the frequency of the acceleration, λ_(f)represents an electrostatic stiffness coefficient dependent on the saidfourth electrodes (9, 9′) in N·m⁻¹·V⁻², V₁ and V₂ are expressed inVolts, and G equals 9.81 m·s⁻².
 2. Gyrometer according to claim 1, inwhich, the said control means controlling the said fifth electrodes (9,9′) in open loop, the said final resonant frequency f_(y) _(—) _(final)is equal to the frequency f_(x) of the drive mode along the drive axisx.
 3. Gyrometer according to claim 1, in which, the said control meanscontrolling the said fifth electrodes (9, 9′) in closed loop, the saidfinal resonant frequency f_(y) _(—) _(final) is equal to the frequencyf_(x) of the drive mode along the drive axis x.
 4. Gyrometer accordingto claim 1, in which, the said control means controlling the said fifthelectrodes (9, 9′) in open loop, the said final resonant frequency f_(y)_(—) _(final) is equal to sum of the frequency f_(x) of the drive modealong the drive axis x and of a predetermined frequency discrepancyΔf_(y).